This grant focuses on arenavirus pathogenesis (how viruses cause disease) and why during infection some hosts become severely ill and die while others remain relatively unscathed. Lessons learned from lymphocytic choriomeningitis virus (LCMV) are applied to Lassa fever virus (LASV). LASV infects over 300,000 individuals per year resulting in over 20,000 deaths. LASV has been transported by travelers from Western Africa to the USA. Its potential as a weapon of biowarfare is a source of national concern. LASV is placed on the Category A list of microbial agents. My laboratory identified alpha-dystroglycan (-DG) as the host cell receptor for LCMV and LASV and demonstrated preferential localization of -DG on dendritic cells (DCs). We then showed that post- translational modification of -DG by the glycosyltransferase LARGE is absolutely critical for the functional maturation of -DG as a receptor for LASV and LCMV binding, entry and replication. P. Sabeti and colleagues found that mutations in LARGE were common in West African populations of Nigeria and Sierra Leone where LASV infection is endemic, but absent in those populations in West Africa where LASV is not endemic. Polymorphisms of the LARGE allele are present in about 35% of the population where LASV is endemic with about 45% of individuals heterozygous and 16% homozygous for it. Mutations in LARGE are found in LASV survivors. Since high viremia (> 9 logs of plaque forming units [PFU/ml of sera]) is routinely associated with signs of severe LASV infection and death, whereas lower viremia (< 8 logs of PFU/ml or less) with recovery, and the -DG/LARGE complex controls LASV entry and subsequent replication, it is likely that mutations in LARGE shape evolution by favoring survival of the host against this virus. Limiting the amount of virus made provides the host's immune system a window of opportunity to mount an effective anti-LASV immune response thereby preventing severe disease and promoting virus clearance. This grant's purpose is to determine if LARGE mutations are responsible for survival to LASV infection. We will assay cells permissive to LASV infection (DCs/monocytes) that contain LARGE mutations in a functional LARGE enzyme assay, and for virus binding, entry and replication using a LASV Gp/LCMV recombinant virus. The recombinant virus can be used in BSL/2 laboratory and has been shown to bind, enter and replicate in permissive human and mouse cells. Thereafter those DCs and monocytes from individuals having LARGE mutations and displaying altered LASV binding, entry or replication or enzymatic activity will be tested at CDC with wtLASV. The fruits of these studies provide the opportunity to identify forces shaping human evolution in that individuals possessing LARGE mutant alleles are likely selected for resistance to LASV. Further, these studies may also identify surrogate markers to classify susceptible or resistant individuals to this viral infection.